CRYSTAL STRUCTURE OF A SELF-SPLICING GROUP I INTRON WITH BOTH EXONS

Structural highlights

1u6b is a 4 chain structure with sequence from Human. This structure supersedes the now removed PDB entry 1t42. The May 2005 RCSB PDB Molecule of the Month feature on Self-splicing RNA by David S. Goodsell is 10.2210/rcsb_pdb/mom_2005_5. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.

Function

[SNRPA_HUMAN] Binds stem loop II of U1 snRNA. It is the first snRNP to interact with pre-mRNA. This interaction is required for the subsequent binding of U2 snRNP and the U4/U6/U5 tri-snRNP. In a snRNP-free form (SF-A) may be involved in coupled pre-mRNA splicing and polyadenylation process. Binds preferentially to the 5'-UGCAC-3' motif in vitro.[1]

Evolutionary Conservation

Publication Abstract from PubMed

The discovery of the RNA self-splicing group I intron provided the first demonstration that not all enzymes are proteins. Here we report the X-ray crystal structure (3.1-A resolution) of a complete group I bacterial intron in complex with both the 5'- and the 3'-exons. This complex corresponds to the splicing intermediate before the exon ligation step. It reveals how the intron uses structurally unprecedented RNA motifs to select the 5'- and 3'-splice sites. The 5'-exon's 3'-OH is positioned for inline nucleophilic attack on the conformationally constrained scissile phosphate at the intron-3'-exon junction. Six phosphates from three disparate RNA strands converge to coordinate two metal ions that are asymmetrically positioned on opposing sides of the reactive phosphate. This structure represents the first splicing complex to include a complete intron, both exons and an organized active site occupied with metal ions.